Image resizing is a common operation in digital image/video processing. An interpolation process is often involved in resizing. Filters such as box (e.g., nearest-neighbor interpolation), tent (e.g., bilinear interpolation), cubic spline (e.g., bicubic interpolation) and a variety of kernels approximating the sinc function have been popular solutions for image interpolation. Among these approaches, the Lanczos filter, a windowed form of the sinc filter, may provide a sharper output than common bilinear or bicubic interpolation. Moreover, the Lanczos filter may be considered to be an effective compromise in terms of aliasing, ringing, and sharpness compared to other approaches.
For an N-lobed Lanczos-windowed sinc function, its oscillation nature can induce a ringing effect and the negative values in the resulting kernel can produce undershoot (i.e., the output is lower than the input). The ringing effect often appears as artificial rings near edges.